1. Technical Field
The present invention relates to remotely controlled television cameras and, more particularly, to very small television cameras capable of being utilized in pipeline inspection applications, which cameras are remotely controllable to vary the field of view, focus and opening of the camera lens. Although the television camera of the present invention has been developed primarily for use in visual inspection of pipeline interiors, it will be understood that the camera has a considerably wider range of applications.
2. Description of the Prior Art
It is known in the prior art to utilize television cameras to visually inspect the interiors of pipelines for leaks, defects, etc. An example of such utilization may be found in U.S. Pat. No. 3,750,711. Prior art television cameras used for this purpose tend to be too large to be utilized in narrow diameter pipelines, particularly when one considers that an illumination source must be provided with and attached to the camera. Attempts have been made to reduce the size of television cameras so that they may be useful for small pipelines, but such attempts have been commercially unsuccessful because of sacrifices that must be made in order to reduce the camera size. Specifically, for pipeline inspection applications, the camera must have a lens that is movable to direct the viewing coverage, or field of view, over the 360.degree.-circumferential interior of the pipe. In addition, the focus and opening of the lens must be adjustable. All of these parameters must be controllable from a remote location at which the television image is viewed and from which the position of the camera in the pipeline may be controlled. Thus, it is possible to provide extremely small cameras without any capability of lens pan or tilt movement; however, a very wide angle lens must be employed to permit viewing over 360.degree. of the pipe interior. Such very wide angle lenses produce significant distortion that is unacceptable for many applications.
Another consideration involved in reducing the size of a pipeline inspection camera is the need to permit independent control of pan and tilt movement of the lens, the focus of the lens, and the lens opening. It is not acceptable, for example, to permit the focus of the lens to be adjusted only in certain pan/tilt positions of the lens; or to permit the lens to be panned only for a particular tilt angle of the lens; etc.
The advent of CCD (charge-coupled devices) image transducers has permitted television cameras to be fabricated in very small sizes. The CCD detector assembly is positioned to receive optical images from the camera lens so that it can convert the components of the received image to corresponding electrical signals. Electrical circuitry associated with the detectors converts the image component signals to standard video signals for use by television receivers/monitors. Even with these CCD cameras, however, the degree of camera size reduction is limited because the CCD detectors must be positioned to receive the focused optical image from the lens. If the lens is to be movable, the CCD detectors and the CCD assembly must therefore also be movable. The result is that the weight of the CCD assembly puts a heavy burden on the pan and tilt motors. In addition, the size of the CCD assembly occupies so much space as to either limit pan/tilt range or limit the degree of size reduction that is possible.